Yeah, there is no grounds for a lawsuit here. They did not lose the kid, so unless he was on his way to a heart transplant, a refund is about as far as it would go.

We have grown adults get on the wrong flight on a regular basis (due the confusing layout of our commuter terminal). They usually tune out all the announcements until the one that says "We are beginning our gradual descent into ABQ..." and then throw a fit because they wanted to go to SFO. Although one guy was smart enough to figure it out in cruise because the sun was on the wrong side of the airplane.

I also diverted once on a stormy night in New England...with a UM, to a town where we did not have ground handling. That one was touchy...we didn't want to leave the kid alone in his own room, and we didn't want him spending the night alone with a grown man. We got a room with two beds and a cot. The CA and FA slept in the beds and the kid slept on the cot